Actually I had this issue on first boot after installing from the June ISO. I spawned a kconsole by keybind, and was able to run commands including the web browser from the terminal, just on a black background without kwin running (no panel, no click on desktop,etc) I laid it down to Wayland issues, because when I rebooted and switched to STD X session Plasma, everything was normal.
However, afterwards I was able to run in Wayland mode fine...dunno?